docs: def window(self):
          """GUI window for Watermark parameters input."""
          platform = system()
          # Tabbed layout for Windows
          if platform is 'Windows':
              layout_tab_1 = []
              layout_tab_1.extend(header('PDF Watermark Utility'))
              layout_tab_1.extend(self.input_source())
              layout_tab_1.extend(self.input_text())
              layout_tab_1.extend(self.input_encryption())
              layout_tab_1.extend(self.footer())
  
              layout_tab_2 = []
              layout_tab_2.extend(self.input_watermark_settings())
  
              layout = [[gui.TabGroup([[gui.Tab('Document Settings', layout_tab_1),
                                       gui.Tab('Watermark Settings', layout_tab_2)]])]]
              window = gui.Window('PDF Watermark Utility', auto_close=False)
              button, values = window.Layout(layout).Read()
              window.Close()
              return button, values, platform
  
          # Standard layout for macOS
          else:
              layout = []
              layout.extend(header('PDF Watermark Utility'))
              layout.extend(self.input_source())
              layout.extend(self.input_text())
              layout.extend(self.input_watermark_settings())
              layout.extend(self.input_encryption())
              layout.extend(self.footer())
              window = gui.Window(TITLE, default_element_size=(40, 1), auto_close=False)
              button, values = window.Layout(layout).Read()
              window.Close()
              return button, values, platform